Seasonal Climate Outlook Message for May to August 2004

The bottom line

El Nino Watch Continues 12/05/04

According to the Bureau of Meteorology "El Nino Wrap Up" (dated 11th May), current ocean and atmospheric conditions across the Pacific continue to remain in a neutral pattern.

However, there still remains a higher than normal risk of an El Niño developing this winter. What happens through to the end of June/early July will be quite crucial in terms of El Niño development. If a trigger event such as westerly wind bursts or a Kelvin wave fails to occur, the likelihood of an El Niño event developing will drop.

During autumn and winter, Kelvin Waves and strong westerly wind bursts across the eastern Pacific are considered to be potential triggers for El Nino events.

It was the strong westerly wind bursts recorded in March/early April this year that initiated a Kelvin wave in the Pacific Ocean. This in turn triggered some subsurface ocean warming in the central Pacific. As Kelvin waves take about two months to cross the Pacific, sub-surface temperatures will need to be watched over the next month for further signs of warming especially in the eastern Pacific (one of the signs of a developing El Nino).

Ocean and coupled ocean/atmosphere forecast models are used to show likely sea surface temperature (SST) patterns out to 9 months. Of 11 models that forecast out to September, 8 indicate a continuing neutral SST pattern while 3 suggest the potential development of an El Nino (or warm) SST pattern. The Bureau of Met has a good summary of these forecast models including their own POAMA model at

While it is positive news that most of these models highlight a continuing neutral SST pattern (rather than an El Nino), given current conditions our policy remains to recommend caution when considering the longer term outlook especially in regard to property management decisions.

Management decisions shouldn't based entirely on one factor (such as the seasonal outlook). As always, any factor that could impact of the outcome of a decision (such as soil moisture levels, soil type, crop, commodity prices, finance, costs, seasonal outlook etc) should be considered.

As there remains considerable uncertainty about the seasonal outlook after July, it may therefore be useful for businesses to consider now what risk management strategies they could use if the likelihood of an El Nino event increases.

The SOI has continued to fluctuate quite strongly. As of the 12th May the 30day average of the SOI is plus 4.6. This is a remarkable rise in value considering the monthly value of the SOI for April was minus 16.1.

It will be very interesting to see if this rise in value is maintained through to the end of the month when the new seasonal outlook is developed or will it fall back into negative values. A fall back into negative values would create a corresponding drop in rainfall probabilities across eastern Australia for the following 3 months.

Last updated: 11 May 2004